TDD Full Coverage Overview Test-Driven Development with full code coverage. Core principle: If you didn't watch the test fail, you don't know if it tests the right thing. Announce at start: "I'm using TDD to implement this feature." The Iron Law Wrote code before a test? Delete it. Start over. Red-Green-Refactor Cycle RED: Write Failing Test Write ONE test for ONE behavior. Verify RED: Watch It Fail MANDATORY. Never skip. Confirm: - Test FAILS (not errors) - Fails for EXPECTED reason (feature missing, not typo) - Error message is what you expect If test passes → You're testing existing behavi…